The invention relates to a pad-printing ink cup fitted with at least one magnet.
A pad-printing ink cup is known from the European patent document EP 0 347 762 B 1. In a pad printing machine, the ink cup sits on a printing plate containing recesses in the form of a print picture to be transferred. The ink from the ink cup penetrates the recesses. The printing plate is displaceable underneath the ink cup and as a result the recesses constituting the picture to be transferred a first time shall be situated underneath the ink cup and another time underneath a printing pad (tampon). The pad is lowered onto the ink-filled recesses from which it removes the ink and hence the print image which it transfersxe2x80x94once the printing plate has been moved out of the pad""s vicinityxe2x80x94onto an object to be printed. A pad printing machine is known for instance from the European patent document EP 0 315 769 B 1, (U.S. Pat. No. 4,905,594).
The following documents contain further state of the art: DE 196 44 366 A1; DE 195 02 802 A1; DE 42 10 521 A1; DE 40 15 684 A1; EP 0 945 266 A1; WO 99 07 556 A1 and WO 93 04 862 A1.
Printing plates illustratively are made of metal or plastic.
Depending on the printing-plate surface material, a hard or soft ink cup doctor edge, shall be advantageous. The doctor edge may be constituted by the very wall of the ink cup or by means of a doctor ring affixed to the ink cup wall. The doctor edge may consist of a metal, a plastic or ceramic or another material.
Depending on the material of the printing-plate surface and of the doctor""s edge, this edge may be pressed more or less hard against said surface to prevent ink from leaking between the doctor edge and the printing-plate surface. The higher the printing rate (image transfer from printing plate to an object being printed), the more rapidly the ink cup must be moved above the printing plate. However speeds entail dynamic pressures inside the doctor and there will be a commensurate danger of the ink leaking between the printing-plate surface and the doctor edge, or that it will float on the printing-plate ink (aquaplaning). As a result, and depending on the materials of the doctor edge and printing-plate surface and on the printing rate, the doctor edge may have to be pressed harder against the printing-plate surface in order to avoid unduly high friction on one hand and on the other hand to assure cleanly wiping the ink from the printing-plate surface.
This problem is solved by a pad-printing ink cup fitted with a cup structure open at its bottom and at the lower end of its wall with a doctor edge to wipe the ink off a printing plate, and further fitted with a magnet situated in the lower zone of the ink cup to attract this ink cup against the printing plate, the ink cup being characterized in that the minimum of one magnet is displaceable relative to the plane of the doctor edge to assume different heights from the plane, the magnetic force effective in the doctor edge plane varying with height.
In particular the invention offers the following advantages:
The invention allows adjusting in simple manner the magnetic force by which the doctor edge is attracted against the printing-plate surface. In this manner the compression of the doctor edge against the printing-plate surface can be matched to various materials which in practice are used for the doctor edge and/or the printing-plate surface. Moreover the compression against the printing-plate surface can be matched to the various viscosities of the inks in the ink cup and deposited by said ink cup on said plate. Thus the same ink cup can be used for different kinds of printing plates. Henceforth it will no longer be necessary to use different ink cups for different printing plates. Advantageously the doctor edge shall be an exchangeable element allowing affixing different doctor edges to the ink cup wall to match different kinds of printing plates and different kinds of inks or ink viscosities.